Numerous simple visual test devices have been developed for the analysis of body fluids in order to determine component analyte amounts. These tests include such devices as means for detecting glucose or other sugars in urine or in blood as well as protein in urine, ketones, uric acid, phenylalanine or enzymes, only to mention a few. All of these tests detect various soluble analytes.
Yet, it has been particularly difficult to perform visual tests of these constituents in whole blood. This difficulty lies in the problems associated with visual responses to the presence of red blood cells in whole blood. The dense red coloration of red blood cells and hemoglobin seriously interferes with such analysis.
Means have been proposed for separating and removing highly colored red cell components from whole blood prior to analysis. Some of the simpler methods involve the use of a carrier member impregnated with a test reagent composition and coated with a semipermeable membrane which effectively acts as a means for screening out large molecules such as hemoglobin. This semipermeable membrane permits the passage of smaller molecules or ions in the solution. A substantially clear fluid containing the constituent diffuses into the test reagent in the carrier to cause a chromogenic reaction with the reagent.
Other methods provide for the drawing of whole blood, then allowing the blood to clot. Once clotted, the blood is centrifuged to separate cell components.
These methods are cumbersome and generally laborious and require at least one extra manipulative step such as wiping, blotting or rinsing with water. This amounts to considerable loss in time and more importantly, accuracy and efficiency. Moreover, the membrane screens out larger molecules in solution, which precludes these molecules from reaching the test reagent. This sometimes renders these methods inoperative for particularly needed determinations. These methods are also technique-dependent and difficult for untrained operators to perform.
Other methods have included taking whole blood samples and placing such samples on a bicomponent reagent strip. After a predetermined time period lapses, the blood sample is blotted to remove excess blood. At that point, constituents of the whole blood sample react with molecules in the reagent strip, and a visual comparison test is performed.
Other test systems may comprise a single matrix which contains both a separating reagent and a test reagent in such a way that the whole blood first contacts the separating reagent to form a substantially colorless fluid which then contacts the test reagent. In employing such a single matrix test system the separating reagent must be compatible with the test reagent for both reaction and stability during storage. The matrix must be designed so that the blood sample reaches the area of the device where the response is read substantially free of any blood coloration. In such an embodiment, a porous support is first coated or impregnated with the test reagent and subsequently the surface of the matrix is coated or impregnated with the separating reagent. In such a test device, the whole blood is contacted with the separating reagent and the test response is observed in an area not initially contacted with the blood and to which the substantially colorless fluid or serum has migrated.
Examples of such single matrix test strips included separating reagents which have been found to be, among other things, water-soluble salts, amino acids and carbohydrates such as mannitol. Some of these chemicals cause hemolysis which releases cellular constituents, including hemoglobin. The salts found effective as separating reagents are non-volatile and do not decompose to any extent under the conditions of preparing and utilizing the test device. The salts have been defined as having solubility in distilled water of at least about 1 gram per liter at 20.degree. C.
In many instances, red blood cells or hemoglobin continue to seep through the separating reagent so that the test reagent encounters colored blood components. When this occurs, accuracy levels are destroyed, and visual comparison is difficult.
It is thus an object of the present invention to provide a unitary test device, wherein during one step the user can apply an unmeasured sample of whole blood and determine analyte levels in the whole blood sample.
It is therefore another object of the present invention to provide a unitary test device wherein the test device, whether single or multi-layer, contains separating means as well as test reagent.
It is a further object of the present invention to form a test device consisting of a single matrix wherein whole blood samples can be applied to one side and visual comparisons of analyte levels can be made at the opposite side of the test strip, or alternatively in a longitudinal transport device, such readings made on a second portion of test strip after wicking.
It is yet a further object of the present invention to determine glucose levels in whole blood samples where a wholly unmeasured sample of whole blood is applied to a single side of a reagent strip. The separating reagent and test reagent are coated on or trapped within the reagent strip and both work effectively and simultaneously to separate and react with the separated clear fluid sample in order to determine, visually, glucose levels of the wholly unmeasured whole blood sample.
It is finally an object of the present invention to provide a test device such that whole blood is analyzed in a single manipulative step for selected molecular constituents such as glucose by a combination of separation means and detection means.